Method for computing main, flash and bump exposures for direct screening

ABSTRACT

In a graph of experimental values giving as parameters the highlights, intermediate tone and shadow densities of the original and dot percents corresponding thereto respectively, curves representing the relations between the dot percent and the density of the original at varying bump exposure percents and varying amounts of flash exposures are shifted in parallel to concentrate their 50% points at the 50% point of the curve representing the case in which only main exposure is made to obtain graphs showing the relation between the dot percent and density difference. Approximate general equations of lower degree are derived from the resulting graphs to obtain equations of lower degree relating to bump exposure, main exposure and flash exposure for digital calculation. A computer includes circuits for electrically digitally calculating the equations. The parameters are fed in the desired combination to the computer for the calculation and indication of the results.

United States Patent I [191 Kosaka [451 Dec. 24, 1974 [75] Inventor: Takeshi Kosaka, Sakai, Japan [73] Assignee: Minolta Camera Kabushiki Kaisha,

Osaka, Japan [22] Filed: Jan. 30, 1973 [21] Appl. No.: 327,919

[30] Foreign Application Priority Data Feb. 4, 1972 Japan 47-l2972 [52] [1.8. CI 235/1513, 95/l.l,' 235/647, 355/35, 355/83 [51] Int. Cl G06f 15/20, G03b 27/78 [58] Field of Search 444/1; 235/1513, 64.7;

[56] References Cited UNITED STATES PATENTS 3,484,165 12/1969 Denner 355/67 3,640,623 2/1972 Florsheim, Jr. et al 95/10 A 3,719,806 3/1973 Davidson 235/647 IP L METHOD FOR COMPUTING MAIN, FLASH AND BUMP EXPOSURES FOR DIRECT SCREENING Primary Examiner-Malcolm A. Morrison Assistant Examiner lerry Smith Attorney, Agent, or'FirmWoldcr 8L Gross [57] ABSTRACT In a graph of experimental values giving as parameters, the highlights, intermediate tone and shadow densities of the original and dot percents corresponding thereto respectively, curves representing the relations between the dot percent and the density of the original at varying bump exposure percents and varying amounts of flash exposures are shifted in parallel to concentrate their 50% points at the 50% point of the curve representing the case in which only main exposure is made to obtain graphs showing the relation between the dot percent and density difference. Approximate general equations of lower degree are derived from the resulting graphs to obtain equations of lower degree relating to bump exposure, main exposure and flash exposure for digital calculation. A computer includes circuits for electrically digitally calculating the equations. The parameters are fed in the desired combination to the computer for the calculation and indication of the re sults.

2 Claims, 12 Drawing Figures PATENTED R SL857. O24

SHEET 10F 5 Fig.

PRIOR ART Fig.2

PRIOR ART DOT PERCENTAGE DENSITY (LOGARITHM OF EXPOSURE) Fig.3

PRIOR ART PATENTED UEC24 I974 SHEET 2 OF 5 PRIOR ART 04% Eg suRE /0 PRIOR ART D DENSITY Fig 7 PRBOR ART dFG *D DENSITY (LOGARITHM OF EXPOSURE) F I g. 6 PRIOR ART mos. Zmumma POO B sec (LOGARITHM OF EXPOSURE) PATENTEDUEBZMW a; 857, 024

SHEET 3 BF 5 V BUMP 0/ oz EXPOSURE DOT PERCENTAGE {Mn Dmh DENSITY DIFFERENCE mm, mm

PATENTEU DEC 2 4 I974 SHEET e 0? 5 m n i mm xl e fm z e zii H METHOD FOR QOMP UTING MAIN, FLASH AND BUMP EXPOSURES FOR DIRECT SCREENING BACKGROUND OF THE INVENTION The present invention relates to a method for computing main, flash and bump exposures for direct screening in converting the varying densities of the original copy to a plurality of dots of various sizes to copy. a color positive original by lithography, letterpress for intaglio.

As already known, flash, main and bump exposures have to be made for the direct screening of positive originals. These exposures are intended to reproduce the shadows, intermediate tones and highlights of the original at suitable densities respectively to obtain a copy more beautiful than the original.

However, flash exposure not only compensates for the tones of shadows but also somewhat influences the intermediate tones, whereas bump exposure compensired, accordingly, it is necessary to clarifythe relationships between the three kinds of exposures and to determine the amountsof the respective exposures so as 16563/1967, now Japanese Pat. No. 510,722. According to the disclosed method, bump exposure percent, the ratio of bump exposure to main exposure, is determined in accordance with the difference between the intermediate tone density and the highlight density of the original, with. flash exposure being determined based on the difference between the shadow density and the intermediate tone density. The influence of the bump and flash exposures on the intermediate tone area is calculated in terms of density of increment of main exposure, and the main exposure is determined at a value obtained by subtracting the-calculated density from the density of the intermediate tone area.

The highlight density, intermediate tone density and shadow density herein referred to are measured densities'of the selected portions of the original which give highlight dots, 50% dots (intermediate tone dots) and shadow dots in a dot plate obtained. The dot plate may be a screened positive or screened negative but, for direct screening, the screened negative is used. The transparent portion of the screened negative forms the plate. The varying sizes of the dots are expressed by the areas of the dots in percent per unit area. FIG. 11 illustrates negative dots of varying percents for comparison. The highlight area gives forexample 10% dots, and the shadow area 90% dots.

Basically, the aforementioned invention of the prior art uses graphs prepared by accurately plotting experimental values to show the relation of the bump exposure percent to the difference between the intermediate tone density and highlight density, the relation of flash exposure to the difference between the shadow density and intermediate tone density, and the relation of the bump exposure and flash exposure to the degree of the influence exerted by bump exposure and flash exposure on intermediate tone density so as to determine the amounts of the respective exposures. The complex relations may be computed by analog method using a special slide rule as disclosed in the same invention and Publications of Japanese Pat. applications No. 2430/1970 and No. 27430/1971 now Japanese Pat. Nos. 577,989 and 637,172 respectively, which are improvements over the invention.

The invention described thus requires a very complex method for computing accurate amounts of the respective exposures, so that everyone skilled in the printing art can not always conduct the calculation readily. The same drawback will still remain even if the relatively simplified slide rule is used as described in the foregoing publications. Moreover, due to the restriction on the construction of the slide rule or computing apparatus, the dot percents for highlight, intermediate tone and shadow areas must be set at limited specific values for example at 10%, 50% and Thus it is entirely impossible to calculate the exposure amounts based on the desired combination of the percentage settings and therefore to fullysatisfy the need to obtain copies more beautiful than the original. The proposed method fur-.-

ther involves the possibility of erroneous use of the slide rule and variations in the accuracy of calculation.

' SUMMARY OF THE INVENTION An object of this invention is to provide a method for computing bump exposure percent, main exposure and flash exposure amounts in accordance with the desired combined conditions of the density of the original, dot percents for highlight, intermediate tone and shadow areas by digital systemwith high accuracy and within a short period of time.

Another object of this invention is to obtain general equations representing ,the relations between the respective exposures for digital calculation in the form of approximate equations of lower degrees, i.e., linear and quadratic equations which assure requisite and sufficient accuracy for practical purposes.

Another object of this inven'tion is to simplify the construction of a computer for the digital calculation by providing the general equations as approximate equations of lower degrees.

According to the present invention, graphs obtained by plotting experimentalvalues of flash exposure and bump exposure are approximately represented by general equations and, based on the general equations, digital calculation is conducted.

Thus the amounts of the respective exposures can be calculated from the general equations by suitably selecting parameters given to the equations, hence very useful in producing copies more beautiful than the original. According to this invention, the general equations may be adopted as desired in the form of approximate equations of lower degrees, which assure satisfactory accuracy in practice and simpify the construction of the computer. i

The present invention enables anyone skilled in the printing art to conduct calculation with ease and high accuracy and within a short period of time. In adition, it is no longer necessary to limit the dot percents to specified values for the determination of the respective exposure amounts but the dot percents may be set at the desired values in combination.

For the digital calculation, this invention employs electric means. Theoretically, the digital calculation by electric means may be made even if the general equations therefor are very complex, but a computer of a large and complex construction will then be needed. However, the use of approximate equations of lower degrees in this invention serves to render the computer greatly simplified in construction, compact and easy to operate.

Other objects and features of this invention will become more apparent from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTIONOF THE DRAWINGS FIG. 1 is an enlarged diagram showing dots in the screened negative at varying percents;

FIG. 2 is a graph showing the relation, as determined by experiment, between the density of the original and the dot percent of screened negative obtained when only main exposure is made;

FIG. 3 is' a perspective view schematically showing the mode of making a main exposure;

FIG. 4 is a graph showing the relation between the density of the original and the dot percent of screened negative at varying bump exposure percents when highlight exposure is made in addition to main exposure, the graph being based on experiment;

FIG. 5 is a perspective view schematically showing the mode of making a highlight exposure;

FIG. 6 is a graph based on experimental data and showing the relation between the density of the original and the dot percent of screened negative at varying flash exposure amounts when flash exposure is made in addition to main exposure;

FIG. 7 is a perspective view schematically showing the mode of making a flash exposure;

FIG. 8 is a graph showing the relation between the density of the original and the dot percent of screened negative at varying bump exposure percents, the curves representing the relation being concentrated at a point at a dot percent of 50%;

FIG. 9 is a graph showing the relation between the bump exposure percent and the slope of its approximate linear equation;

FIG. 10 is a graph showing the relation between the density of the original and the dot percent of screened negative at varying flash exposure amounts, the curves representing the relation being concentrated at a point at a dot percent of 50%;

FIG. llv is a diagram showing an example of flow chart of a computer; and

FIG. 12 is a diagram showing an example of operation panel of the computer.

DESCRIPTION OF THE PREFERRED EMBODIMENT For color printing at least four color plates are used which are inked in yellow (Y), magenta (M), cyan (C) and black (B) respectively and which are prepared from four screened negatives obtained from an original of the reflecting or transparent type. It is therefore necessary to produce a screened negative to prepare each color plate.

FIG. 2 shows the relation between the density D of an original and dot percent, i.e., the percentage of dots formed in a screened negative when only main exposure is made, the former being plotted as abscissa, the latter as ordinate. The main exposure is made by forming the image of an original 3 on the face of a negative film 1 through an optical system 4, with a screen 2 disposed in front of the film 1 as seen in FIG. 3. The optical system 4 of course includes an unillustrated color separation filter. When only the amountof light for illuminating the original 3 is varied to make the same exposure under the same conditions with respect to the optical system 4 and the like, the curve on the graph of FIG. 2 can be moved along the abscissa in parallel as shown in the graph. Through such procedure, a certain density of an original can be converted to a screened negative having the desired dot percent. To determine the dot percent. an expert measures the density of a selected portion of the original which is to be used as an intermediate tone area. The density is such that it will give the dot percent of 50%. However. this means that a certain density among the varying densities of the original will be converted to the dot percent setting for example of 50%, but it is not known to what percents the other densities will be converted. In other words, it is impossible to produce a copy which is more beautiful than the original only by main exposure. For this reason, bump exposure and flash exposure are made in addition to the main exposure for the adjustment of highlight and shadow areas as already described.

FIG. 4 is a graph showing the results of an experiment in which bump exposure is made in addition to the main exposure, the density D of the original being plotted as abscissa vs. dot percent as ordinate. For bump exposure, the screen in front of the negative film 1 is removed and the image of the originalis formed on the film surface through the optical system 4 as shown in FIG. 5.

In the graph of FIG. 4, bump exposure percent (a) is used in place of bump exposure. The bump exposure percent is the rate of the amount of bump exposure relative to the main exposure. The graph shows the relation between the density of original and dot percent of screened negative at the bump exposure percents of 0%, 5% and 10%. The bump exposure percent of 0% indicates the case in which only main exposure is made, and the resulting curve coincides with the curve of FIG.

It will be seen from FIG. 4 that the change of bump exposure percent from 0% to 5% results in the corresponding variation in the density of the original, especially in the highlight density. By utilizing this phenomenon, a highlight density selected from among the densities of the original can be converted to the dot percent set value. Thus, the bump exposure is used to convert the difference Dmh between the intermediate tone density Dm and the highlight density Dh to a controlled degree of difference in dot percent. In other words, when a dot percent is set for the highlight area and the difference between the selected intermediate tone density of the original and the highlight density is known,

FIG. 6 is a graph showing the results of an experiment in which flash exposure is made in addition to main exposure, the density D of the original being plotted abscissa vs. the dot percent of screened negative as ordinate. As seen in FIG. 7, flash exposure is made by projecting weak light to a film l uniformly over its entire surfacefwith a screen 2 disposed in front of the negative film but without the original. The exposure is made using a light source other than one for the main exposure. The amount of flash exposure is expressed in terms of exposure time [3 (second). The curve for a flash exposure of second represents the case in which only main exposure is made, the curve matching the curve of FIG-2. I

FIG. 6 reveals that variations in the amount of flash exposure influence the density of the original, particularly the density of its high density portion (shadow area). This phenomenon is utilized to convert a shadow density selected from among the densities of the original to the desired dot percent setting. If the dot percent for the intermediate tone area is set at 50% and a dot percent is set for the selected shadow area, the desired amount of flash exposure can be determined by the difference Dsm between the selected shadow density of the original and the intermediate tone density'as in the foregoing. The flash exposure also influences the intermediate tone density as indicated at dFB in .FIG. 6.

If bump exposure and flash exposure were not made, the amount of main exposure would be read on the abscissa of the foregoing graph of FIG. 2.at the exposure amount corresponding tothe intermediate tone density of the original (the intermediate tone density described with reference to FIG. 2) but, in practice, bump expo sure and flash exposure are always made. Accordingly, the requisite main exposure amount is obtained by subtracting from the above-mentioned main exposure amount an excess amount of exposure given by flash and bump exposures to the intermediate tone area.

The effects of the bump exposure and flash exposure on the intermediate tone density can be known as the increments of density of the original from the graphs of FIGS. 4 and 6. Furthermore, the increments can be calculated inasmuch as they are functions of the respective amounts of flash exposure and bump exposure. Consequently, if the required amounts of bump exposure and flash exposure are given, the desired amount of main exposure will be determined. Since the required amount of bump exposure is based on the amount of main exposure before compensation, it may be eventually determined from the main exposure amount after compensation, namely from the requisite main exposure amount.

Based on analyses, the present invention basically provides general equations for computing the bump ex-' posure percentage 11, flash exposure amount [3 and main exposure amount Mm by digital calculation from the foregoing dot percents and densities of the original (the differences between the intermediate tone density at the base level, e.g., at 50% and the highlight and shadow densities). Further detailed description will be given below. i Calculation of Bump Exposure Percent The graph of Flg. 8 corresponds to part of the graph of FIG. 4 with the dot percent ranging from 0 to 50%.

. b the intermediate tone density Dm and highlight density plotted as abscissa vs. dot percent as ordinate.

It will be seen from the graph that if the bump exposure percent a can be analytically represented by the formula rx=f(Dmh, dot percent) (1), the percent a will be determined by digital calculation. Conventionally, a was determined from Dmh and dot percent only by reading the graph or by using a slide rule or like means on which'the dot percent is set at specific values as disclosed in Publication of Japanese Pat. application No. 16563/1967 referred to above. Further it is impossible to caluculate the bump exposure percent from the equation (1) by giving a desired value as dot percent.

The inventor has found that the relation between the dot percent and density difference Dmh when bump exposure is made can be approx'imated,-with sufficient accuracy for practical use, to the linear equation of y Ax B at a dotpercent given by a bump exposure percent in the range of 0 to 30% which range is empirically found almost satisfactory in practice, and that the relation of a quadratic equation exists, with sufficient accuracy for practical use, between the bump exposure percent a and the slope A of the linear equation as indicated in the graph of FIG. 9; Further the relation of a linear equation has been found to exist between the bump exposure percent or and the intercept B of its linear equation. Thus-a general formula can be obtained for digital calculation.

It is noted that if the curves of FIG. 8 are approximated by an approximate equation of a higher degree, the degree of the resulting approximation will of course be higher than would be achieved by a linear equation, but the relation between that equation and bump exposure percent will then become very complex, making it necessary to use a complicated method of digital calculation and a complex computer. Moreover there is no difference in accuracy between the linear equation and equation of a higher degree from the viewpoint of practical use.

. For this reason it follows that for practical purposes approximation to a linear or quadratic equation gives better results in various aspects for instance in simplifying the construction of computer. On the other hand, it is possible in very limited cases to approximate the relation between the bump exposure percent and slope A to a linear equation, but in practice it is necessary to approximate the relation to a quadratic equation to assure accuracy.

More specifically, if auxiliary X-axis and Y-axis are provided for FIG. 8 and the curves in FIG. 4 are shifted horizontally in parallel to concentrate the 50% points of the respective curves at the dot percent point of 50% of the main exposure, therelation between the dot percent and Dmh will be represented, with sufficient accuracy for practical use, by a graph of the equation: y Ax B (2). From the graph of FIG. 9, the following relations are found to exist between the bump exposure percent or and the slope A of the curve and intercept B across Y-axis.

A=l 'a +I 'u-l-l (3) wherein l l I are constants. Between y and W (dot percent at a bump exposure point) there is the relation of y l -Yh Z and between x and Dmh l -Dmh wherein l and 1 are constants, so that if a is expressed by Dmh and Yh, equations (2) to (6) give a l/Dmhj a,a -Dmh V' a (a a 'Yh)Dmh a 'Dmh 7 wherein a a a are constants. Thus a general equation will be obtained with respect to a. As to the portion V in equation (7), the expansion of the root can of course be taken up to the desired term to obtain an approximate value. Calculation of the Amount of Flash Exposure As in FIG. 8, FIG. 10 has auxiliary X-axis and Y-axis andcorresponds to part of FIG'. 6 which covers the dot percent range of 50 to 100%. The curves in FIG. 6 are shifted horizontally in parallel to concentrate their 50 dot percent points at the 50% point given by main expsoure. The graph represents thedensity difference Dsm between shadow density Ds and intermediate tone density Dm as abscissa vs. dot percent for shadow area as ordinate and shows the relation between the Dsm and dot percent at varying flash exposure amounts basedon experimental data. To determine the flash exposure amount B by digital calculation; it is necessary to 0bfilm to the outer periphery of a bundle of rays. The energy E0 of'light (amount of light x time) to give a definite density to the original is where I0 is current applied to the electronic flash for the production oflight, To is the duration of single flash of light and Mx is the frequency of flashes produced by stroboscopic flash for the main exposure.

Supposing that a thin lens system is used in which distance from original to image-forming lens is a, distance from the image-forming lens to the film surface is b, focal length of the image-forming lens is f and photography magnification is N,

(1/ and bla N which give If the line through the center point of the lens at right I angles to the ray passing through the outermost portion of the lens has a length h and diaphragm aperture value tain,- as in the foregoing case, an analytical equation in the form of r I B f( Dsm, dot percent) The present inventor has found that the relation between the Dsm and dot percent can be approximated, with sufficient accuracy for practical use, to a linear equation within the dot percent range of 100 to 60% and that the relation between the slope of the linear equation and-the flash exposure'amount B can be approximated with'sufficient accuracy for practical use. Thus by the same procedure as in the case of the bump exposure percent a, the following general equation has been obtained:

wherein Ys is the'dot percent for the shadow area and b b b and b., are constants.

bump exposure percent a and flash exposure amount B can be given by digital calculation.

where B, is the brightness of .the original and 6 is the angle between the optical axis of the image-forming lens and a line extending from the center point of the v In this way, general equations are obtained by which for photographing by main exposure is Fx,

' Fx f /2h and therefore sin 0= h/b l/2Fx(N 1 From equation (1 1) If the transmitting rate of the original is lO I 10' l 0''. If the amount of compensation for variation of the negative dot percent from the 50% level in main exposure is 10" and the effect of burn exposure and flash exposure on main exposure is 10 equation (14) gives M1: Fx /Fs 'E-lO -IO' -(N 1W4 -10- 15) where Fs is diaphragm aperture value for setting Mx such that Mx E, E corresponds to speed of the negative film used including developing conditions and l0 is l-(loge l0)A inasmuch as the linear approximation thereof assures sufficient accuracy in practice and is l-loge l0'A+% (loge l0) -A Since the effect 10' of bump exposure and flash exposure on main exposure conceivably has a proportional relation with sufficient accuracy for practice in view of the Supposing that the dot percent set for the intermediate tone area is Ym, the variation of Ym from 50% point is AYm and density gradient approximately corresponding to the intermediate tone of the film is ym, A l/m-AYm Accordingly,

.10-(6200! ca-B) (16) wherein -AYm=Ym-O (17) E Ei-k (18) k=l'-E /l0O- (19 in which Eiwith i of 1, 2, 3 or 4 corresponds to film speed for Y, M, C or B color plate and E is the amount of compensation in terms of percentage which is dependent on developing conditions and the like (and is very infinitesimal relative to-Ei). Since Mm M 'M -M 'IO M Ei'klO M2 1 l/ym-AYm M (N l) /4 it follows that H F /Fs 'Mm'oz/l00 H= F /Fx 'Fx /Fs 'Mm'a/IOO Therefore equation (20) gives I i H F /Fs 'Mx'a/lOO where H is the frequency of flashes of electronic flash for bump exposure and F is a diaphragm aperture value for bump exposure. The frequency of flashes has the same meaning as the shutter speed of the camera.

From equation (20), the diaphragm aperture value for main exposure photography will be lit) equation (25) gives the diaphragm aperture value F for bump exposure The computer of this invention incorporates computing circuits for calculating the foregoing general equations digitally as shown in the flow chart of FIG. 11. The'computing circuits may have constructions already known as in electronic computers. The present computer finally calculates and indicates the flash exposure amount [3, main exposure amount Mx, diaphragm aperture value Fx for main exposure photography, bump exposure amount H, diaphragm aperture value F for bump exposure and bump exposure percent 01.

An input device IP will first be described which comprises a memory unit MM, parameter unit PM, selection key unit SK, inner input unit HP and outer input unit OlP.

The memory unit MM feeds as inputs the constants a a a of equation (7), the constants b b b, of equation (9), permissible reproduction limit c, of development determined by film density, constants c and c of equation 16), conditions E E E dependent on film speed suchas camera, screen, film and de-' veloping conditions and the like, dot percents Ys, Ym

and Yh set for shadow, intermediate tone and highlight areas, photographicmagnification N, frequency Mx of flashes of electronic flash for main exposure photography and frequency H of flashes of electronic flash for bump exposure photography.

The selection key unit SK includes key Y, M, C and B for'feeding the grades of masking for Y, M, C and B color plates, mask selection key MA for the modification of the original and outer input selection key AU.

The inner input unit llP feeds the inputs of densities Ds, Dm and Dh of shadow dot, intermediate tone dot and highlight dot. These inputs are given selectively by manual operation.

The outer input unit OlP are adapted to feed as inputs the densities Ds', Dm' and 10h of shadow dot, intermediate tone dot and highlight dot directly from density measuring means (unillustrated).

FIG. 12 shows an example of operation panel of the computer which includes at its upper portion an indication unit OP for indicating outputs resulting from the calculation, the parameter input unit PM provided with the selection keys and disposed below the indication unit OP, a parameter operation table PMO below the unit PM, and the memory unitMM in the form of a cassette and set in position below the parameter operation table PMO.

The indication unit OP comprises a section for indicating the flash exposure amount [Sin second, another section for indicating the main exposure amount in terms of frequency Mx of flashes of electronic flash unit and diaphragm aperture value Fx, and another section for indicating the bump exposure amount in terms of frequency H of flashes of electronic flash unit and diaphragm aperture value F as above and for indicating the bump exposure percent a.

Disposed between the input device and the indication unit are digital computing electric circuits according to the flow chart of FIG. 11 as already described for giving specified indication outputs to the indication unit in response to the respective inputs. Because these computing circuits can be constructed according to-the prior art, they will not be described herein. The arrows in FIG. 11 represent processing systems for the input signals.

The keys Y, M, C, B, MA and AU of the selection key unit SK are provided for opening and closing gates provided for the computing circuits. The keys Y, M, C and B open and close gates GY, GM, GC and GB for information inputs for the respective color plate filters. The key MA, mask selection key for the modification of the original, switches a changeover gate GMA. The key AU for effecting changeover between the inner input and outer input operates changeover gates GDs, GDm and GDh.

The EM for the computing circuit of 10 X EM in FIG. 11 is a constant for'compensation by masking. The circuit of computing with /3 stop unit (errors within Va stop unit produce no effect on accuracy in practice) gives signals indicating diaphragm aperture values selected from among a plurality of predetermined diaphragm aperture values of the camera which are closest to the calculated diaphragm aperture values of Fx and F respectively.

Operation procedures will now be described.

In the case where the respective densities of highlight, intermediate tone and shadow areas are directly fed from the measuring means, the key AU of the selection key unit SK is depressed to open the outer input gate, whereas if the outer input is not used, the key AU is left intact.

If the outer input is not fed, the above-mentioned densities are measured for the respective color plates and the measured values are fed as inputs. Calculation is conducted for the color plates individually. Selection for this purpose is achieved by depressing the key MA and one of the keys Y, M, C and B which give information inputs from the respective color plate filters.

The measured densities and dot percents set for the respective areas are fed as inputs and the operation key OPE on the operation table PMO is depressed, whereby calculation is conducted for the selected one color plate by the computing circuits according to the flow chart in FIG. 11. To feed the required inputs to the memory unit MM,

cassettes including various combinations of the inputs are previously prepared, and the desired cassette is selected and set in place. The required inputs can then be fed to the memory unit. After the calculation for one color plate has been completed, calculations for the other color plates are likewise conducted in succession.

If a preset frequency Mx of flashes for main exposure photography is fed by depressing the key Mx and numeral keys on the operation table, the set value will be directly indicated on the indication unit, and the main exposure amount will be-calculated and indicated as the diaphragm aperture value Fx.

Further when a preset flash frequency H for bump exposure photography is fed, the diaphragm aperture value F will be calculated and indicated.

If negative results are given for Dsm, Dmh and C -Dmh in FIG. 11, the indication of NO will appear on the indication windows for or or F to indicate incapability of photography.

While an embodiment of the computer has been described above, it will be apparent from the description that various modifications can be made for example in the construction of the input device.

What is claimed is:

l. A method for computing main, flash and bump exposures for direct screening comprising the steps of:

a. preparing a graph of experimental values giving as parameters densities of highlight, intermediate tone and shadow areas of an original plotted re-' spectively against dot percent and parallelly shifting, the curves representing the relation between the dot percent and the density of the original at varying bump exposure percents to concentrate their 50% points at the 50% point of a curve representing the case in which only a main exposure is made and to thereby obtain a graph of bump exposure showing the relation between the dot percent and density difference, b. determining from the graph of bump exposure val- -ues of coefficient to obtain an equation of lower degree for computing a bump exposure percent, parallelly shifting curves in the graph of experimental values representing the relation between the dot percent and the density of the original at varying amounts of flash exposure to concentrate their 50% points at the 50% point of a curve representing the case in which only a main exposure is made and to thereby obtain a graph of flash exposure showing the relation between the dot percent and density difference, d. determining from the graph of flash exposure values of coefficients to obtain an equation of lower degree for computing an amount of flash exposure,

e. forming an equation of lower degree for computing an amount of main exposure from an energy of light providing a predetermined density to the original, the effects of the bump exposure and flash exposure on the intermediate tone area, the sensitivity of a negative film including the conditions for developing the same, the diaphragm aperture value for setting the amount of the main exposure, the

' variation of the dot percent set for the intermediate tone area from the 50% point, and determined coefficients f. forming an equation of lower degree for computing an amount of bump exposure from the amount of main exposure, the bump exposure percent, a film speed foreach color plate and developing condi-v tions, g. forming an equation of lower degrees for computing the diaphragm aperture value for main expo- 13 sure photography from the main exposure amount computing equation,

a h. forming an equation of lower degree for computcomputer incorporating electrical digital computing circuits for calculating'from the equations the main, flash, and bump exposure amounts for direct screening.

2. A method for computing main, flash and bump exposures for direct screening comprising the steps of a. preparing a graph of experimental values giving as parameters densities of highlight, intermediate tone and shadow areas of an original plotted respectively against dot percents and parallelly shifting the curves representing the relation between the dot percent and the density of the original at varying bump exposure percents to concentrate their 50% points at the 50% point of a curve representing the case in which only a main exposure is made and to thereby obtain a graph of bump exposure showing the relation between the dot percent and density difference;

b. determining from the graph of bump exposure values of coefficients-11 m of an equation for computing a percent of bump exposure:

m c. parallelly shifting curves in the graph of experimental values representing the relation between the dot percent and the density of the original at varying amounts of flash exposure to concentrate their 50% points at the 50% point of a curve representing the case in which only a main exposure is made and to thereby obtain a graph of flash exposure' showing the relation betweenthe dot percent and density difference;

d. forming determing from the graph of flash exposure values of coefficients b b,, of an equation for computing an amount of flash exposure:

B b 'Dsm bg'YS b /Dsm e. forming from an energy of light providing a predetermined density to the original, the effects of the bump and flash exposures on the intermediate tone area, the sensitivity of a negative film including the conditions for developing it, the diaphragm aperture value for setting the amount of the main exposure, a photography magnification, the variation of the dot percent set for the intermediate tone area from the 50% point and determined coefficients c and c; an equation for computing an amount of exposure an equation for computing a diaphragm aperture value for bump exposure:

g. feeding the parameters and the sets of determined coefficients in'a desired combination to a computer incorporating electrical digital computing circuits for calculating from the equations the main, flash and bump exposure amounts for direct screening. 

1. A method for computing main, flash and bump exposures for direct screening comprising the steps of: a. preparing a graph of experimental values giving as parameters densities of highlight, intermediate tone and shadow areas of an original plotted respectively against dot percent and parallelly shifting, the curves representing the relation between the dot percent and the density of the original at varying bump exposure percents to concentrate their 50% points at the 50% point of a curve representing the case in which only a main exposure is made and to thereby obtain a graph of bump exposure showing the relation between the dot percent and density difference, b. determining from the graph of bump exposure values of coefficient to obtain an equation of lower degree for computing a bump exposure percent, c. parallelly shifting curves in the graph of experimental values representing the relation between the dot percent and the density of the original at varying amounts of flash exposure to concentrate their 50% points at the 50% point of a curve representing the case in which only a main exposure is made and to thereby obtain a graph of flash exposure showing the relation between the dot percent and density difference, d. determining from the graph of flash exposure valUes of coefficients to obtain an equation of lower degree for computing an amount of flash exposure, e. forming an equation of lower degree for computing an amount of main exposure from an energy of light providing a predetermined density to the original, the effects of the bump exposure and flash exposure on the intermediate tone area, the sensitivity of a negative film including the conditions for developing the same, the diaphragm aperture value for setting the amount of the main exposure, the variation of the dot percent set for the intermediate tone area from the 50% point, and determined coefficients f. forming an equation of lower degree for computing an amount of bump exposure from the amount of main exposure, the bump exposure percent, a film speed for each color plate and developing conditions, g. forming an equation of lower degrees for computing the diaphragm aperture value for main exposure photography from the main exposure amount computing equation, h. forming an equation of lower degree for computing the diaphragm aperture value for bump exposure from the bump exposure amount computing equation, and i. feeding the foregoing parameters and the determined coefficients in a desired combination to a computer incorporating electrical digital computing circuits for calculating from the equations the main, flash, and bump exposure amounts for direct screening.
 2. A method for computing main, flash and bump exposures for direct screening comprising the steps of a. preparing a graph of experimental values giving as parameters densities of highlight, intermediate tone and shadow areas of an original plotted respectively against dot percents and parallelly shifting the curves representing the relation between the dot percent and the density of the original at varying bump exposure percents to concentrate their 50% points at the 50% point of a curve representing the case in which only a main exposure is made and to thereby obtain a graph of bump exposure showing the relation between the dot percent and density difference; b. determining from the graph of bump exposure values of coefficients a1-a6 of an equation for computing a percent of bump exposure: Alpha 1/Dmh (a1 - a2.Dmh + Square Root a3 + (a4 - a5.Yh) Dmh - a6.Dmh2); c. parallelly shifting curves in the graph of experimental values representing the relation between the dot percent and the density of the original at varying amounts of flash exposure to concentrate their 50% points at the 50% point of a curve representing the case in which only a main exposure is made and to thereby obtain a graph of flash exposure showing the relation between the dot percent and density difference; d. forming determing from the graph of flash exposure values of coefficients b1 - b4 of an equation for computing an amount of flash exposure: Beta b1.Dsm - b2.Ys + b3/Dsm + b4; e. forming from an energy of light providing a predetermined density to the original, the effects of the bump and flash exposures on the intermediate tone area, the sensitivity of a negative film including the conditions for developing it, the diaphragm aperture value for setting the amount of the main exposure, a photography magnification, the variation of the dot percent set for the intermediate tone area from the 50% point and determined coefficients c2 and c3 an equation for computing an amount of main exposure: Mx Fx2/Fs2.E.10Dm.(1-1/ gamma m. Delta Ym).(N+1)2/4.10 (c c ) f. forming from the amount of main exposure, the percent of bump exposure and the amount of bump exposure An equation for computing a diaphragm aperture value for bump exposure: FH Fs Square Root H/Ho; g. feeding the parameters and the sets of determined coefficients in a desired combination to a computer incorporating electrical digital computing circuits for calculating from the equations the main, flash and bump exposure amounts for direct screening. 